1. Field of the Invention.
The field of the invention is audio loudspeaker enclosures fitting within the ear pockets of motorcycle helmets or helmets worn in a noisy environment.
2. Description of the Related Art.
In recent years, motorcycle riders have enjoyed vast improvements in communications. This is especially true in respect to communications between the motorcycle driver and passengers as well as other motorcycle drivers and passengers, all while the motorcycles are moving. Such improvements include the installation of microphones proximate the rider's and passenger's mouth by attachment to the motorcycle helmet, as well as the installation of headsets or earphones in both their helmets.
As might well be apparent, the motorcycle driver and passenger are exposed to vast amounts of noise ever present in their immediate environment. In addition to the noise of the motorcycle engine, the road sounds, i.e., sounds of the tires engaging the road, sounds of nearby vehicles including emergency vehicle sirens, the motorcycle rider and passenger are also bothered with the sounds of air rushing past the motorcycle, and past the body, face, and ears. The noise in a motorcycle helmet presents a very special environment in which sound enters the rider's ears.
An electronic circuit connecting to the microphone must, as far as possible, not amplify for transmission the sounds entering the microphone except for the driver's and passenger's speech. Similarly, the sound emitted from the earphones located in the helmets must enter the ear with maximum clarity and minimum distortion as much as possible, at least with respect to factors controllable in construction of the earphones and helmet.
In today's helmets, it is common to line the inside of the helmet with a layer of cushioning material, commonly styrene, and then cover the cushioning material with cloth or other similar lining material. In many cases, the cushioning material may have a thickness of 1/2 to 1 inch. Because people's ears tend to protrude from the head a short distance, it is common to place ear pockets in the cushioning material and liner, ear pockets merely being a void within the cushioning material surrounding the rider's and passenger's ears when the helmet is worn. This is especially true if it is intended to place an earphone or loudspeaker within the ear pocket directing its sound waves into the ear. Commonly, the ear pocket may have a depth equal to the thickness of the cushioning material, extending to the outer plastic, fiberglass, or metal shell comprising the helmet.
In the design of helmets, it would be desirable to have the rider's ear completely within the ear pocket with the surrounding cushioning material coming up very near to the rider's head. However, such a practice would not provide a comfortable helmet, and this is especially true when putting on or taking off the helmet, nor would such an arrangement be safe inasmuch as the ear may well be completely isolated from hearing sounds necessary to be heard, such as nearby emergency vehicles.
Accordingly, a compromise must be reached between how tightly a rider's ear may be encompassed by the ear pocket so as to reduce outside noise whereby the sound emitted from the ear pocket loudspeaker is readily understood, and the allowance of sounds from the outside environment, especially those sounds which may indicate potential danger.
In such respect, advances in motorcycle helmet design have been made in reducing noise coming in from the outside. However, advancement in the state of the art respecting loudspeakers placed into ear pockets has not been as remarkable. For example, it is entirely common today for the loudspeaker assemblies emplaced into the motorcycle helmet ear pockets to be placed within a speaker enclosure, usually a disk shaped container having a loudspeaker inside broadcasting through a plurality of small openings in one of the circular faces, the loudspeaker being immediately behind the circular face. It is also common to place venting holes in the rear circular face of the speaker enclosure in order that the rear chamber within the speaker enclosure and behind the loudspeaker be relieved in order to improve the audio quality output of the speaker. If the rear chamber behind the loudspeaker is completely sealed, then flexing movement of the cone and diaphragm of the loudspeaker has the effect of compressing and decompressing the air in the rear chamber, thus putting considerable constraints upon the frequency response of the speaker cone and diaphram, together with the power needed to drive it. To relieve the problem of compressing and decompressing the air in the rear chamber, the venting openings previously mentioned are placed in the rear face of the speaker enclosure. This bleeds the sound and pressure waves out the back of the speaker enclosure.
However, in using the speaker enclosures that are presently available having the rear venting opening and installing them in the ear pockets, it is noted that there is considerable distortion of the primary sound waves emanating from the speaker enclosure as the sound waves enter the rider's ears. This is especially true in the low frequency range of sounds. The inventor has investigated this sound distortion and lack of clarity and has discovered that substantially the problem lies in the sound waves emitted from the vented openings in rear of the speaker enclosure in that these parasitic sounds, being emitted by the backside of the loudspeaker diaphragm and cone, travel around the speaker enclosure situated within the ear pocket to mix with and distort the primary sounds being emitted directly from the front face of the speaker enclosure. This mixing of sound causes cancellation in some cases, amplification in other cases, all resulting in distortion of the sound waves as they impinge upon the rider's ears. If the back face of the speaker enclosure is sealed, then the primary sound emitted from the enclosure is substantially compromised.
Thus it is very apparent that sound characteristics within a motorcycle helmet environment is considerably different from that presented in ordinary speaker enclosure designs.
It is known to vent the rear chamber of a speaker enclosure by placing openings in the enclosure wall or to place a tube interiorly to the rear chamber which provides open communication to the environment immediately outside the enclosure. The latter is shown in the 1932 patent of Thuras, U.S. Pat. No. 1,847,702. It is also known in earphones of the type adapted to reside within a person's ear to have a duct extending from the housing for the reason of increasing the compliance and/or equivalent mass of the vibration system to reduce the resonance frequency of the earphone. For example, Yamagishi, in the U.S. Pat. No. 4,742,887, provides such a device. Yamagishi additionally provides, at the terminal end of this duct, openings to the environment. A duct is utilized because there are no alternatives to increasing the mass in an in-the-ear earphone. Yamagishi, however, does not provide an earphone for operation in the helmet environment.
It is readily apparent that the sound waves reaching the listener's ears may be obviously enhanced if apparatus were available which prevented the parasitic sound waves exiting the rear of the speaker from coming around the speaker enclosure and mixing with the speaker's primary output sound waves.
It is also obvious that there is need for apparatus which carry away the parasitic sound waves emanating from the rear of the speaker enclosure in a motorcycle helmet ear pocket so that the sound waves do not have the opportunity to travel to the front face side of the speaker enclosure and interfere with the primary emitted sound waves.